This invention relates to refining of ores and more particularly to electro-refining systems and methods.
In electro-refining, semi pure copper anodes are suspended in acid next to a cathode. The anode is given a positive charge of direct current while the cathode is given a negative charge. This charge causes the copper ions to transfer from the anode to the cathode and the impurities fill to the bottom of the tank.
In solvent Extraction-Electro-winning (SXEW) the copper is leached out of the ore, the leachate is concentrated and pumped into tanks similar to electro-refining. The difference is in Electro-winning the copper enters the tank in liquid solution, The anode is not impure copper, it is permanent and usually lead. The direct current voltage between the anode and cathode is greater in Electro-winning than in electro-refining because the dissolving of the impure copper in acid generates some voltage.
In either case the cathode can be permanent, usually stainless steel or titanium, or a starter sheet. The starter sheet consists of a one day deposit of copper suspended from a metal bar, usually copper and immersed in the tank. Copper is deposited on all surfaces of the starter sheet and this copper along with the starter sheet is harvested every 7 to 14 days at a weight of 240 to 400 pounds.
The direct current flowing thru each cathode is quite high, from 350 to 700 amps. Each tank or cell can have from 35 to 60 Cathodes.
As the temperature of the surface of the cathode is increased the rate and quality of copper deposition is increased. Currently all of the electrolyte flowing tbru the cell is heated to keep the surface of the cathode warml When the electrolyte gets too hot the permanent lead anode is degraded and more acid vapors at evolved and enter the atmosphere of the cell house.
In the case of a permanent cathode of stainless steel of titanium, care must be taken to prevent the copper from depositing around the edge and locking itself on the metal. Usually a non conducting edge strip is attached to the cathode to keep the copper off the edges. Wax is sometimes deposited on the bottom edge for the same reason. The wax process is messy and must be cleaned off and redeposited after each harvest of copper.
It is clear that there is a need for an improved electro-refining system. Another Type of metal refining cell is the "bi-polar" cell. In this type of cell the current flows sequentially throu the cell from one end to the other. One side of each metal plate is the anode and the other is the cathode. In the case of SXEW, lead or carbon is bonded to a sheet of stainless steel. A series of these plates are placed parallel to each other ina tank with groves in the sides and bottom to receive them. A direct durrent is induced at one end of the tank and flows from panel to panel to the other end. The new and novel cathode in this invention can be readily adapted the perform in the bi-polar cell by bonding lead, carbon, graphite or some other nobel material on the anode of the panel.